1. Field of the Invention
The present invention relates generally to three-dimensional (3D) graphics and volume visualization, and more particularly relates to an apparatus and method for real time volume processing and universal three-dimensional rendering.
2. Description of the Prior Art
Computer rendering is the process of transforming complex information into a format which is comprehensible to human thought, while maintaining the integrity and accuracy of the information. Volumetric data, which consists of information relating to three-dimensional phenomena, is one species of complex information that can benefit from improved image rendering techniques. The process of presenting volumetric data, from a given viewpoint, is commonly referred to as volume rendering.
Volume visualization is a vital technology in the interpretation of the great amounts of volumetric data generated by acquisition devices (e.g., biomedical scanners), by supercomputer simulations, or by synthesizing geometric models using volume graphics techniques. Of particular importance for manipulation and display of volumetric objects are the interactive change of projection and rendering parameters, real-time display rates, and in many cases, the possibility to view changes of a dynamic dataset over time, called four-dimensional (4D) visualization (i.e., spatial-temporal), as in the emerging integrated acquisition visualization systems.
A volumetric dataset is commonly represented as a 3D grid of volume elements (voxels), often stored as a full 3D raster (i.e., volume buffer) of voxels. Volume rendering is one of the most common techniques for visualizing the 3D scalar field of a continuous object or phenomenon represented by voxels at the grid points of the volume dataset, and can be accomplished using two primary methods: object-order methods and image-order methods. Using an object-order approach, the contribution of each voxel to the screen pixels is calculated, and the combined contribution yields the final image. Using an image-order approach, sight rays are cast from screen pixels through the volume dataset, and contributions of voxels along these sight rays are used to evaluate the corresponding pixel values.
Over the past three decades graphics systems have evolved duofold: from primarily two-dimensional (2D) to 3D and 4D (space and time), and from vector graphics to raster graphics, where the vector has been replaced by the polygon as the basic graphics primitive. This has led to the proliferation of polygon-based geometry engines, optimized to display millions of triangles per second. In such systems, however, triangle facets only approximate the shape of objects. Still, the 3D polygon-based graphics market continues to boom, and has become one of the hottest arenas of the personal computer (PC) industry.
In response to emerging demands placed on traditional graphics systems, various techniques have been devised to handle and display discrete imagery in order to enhance visual realism of the geometric model, as well as enhance or replace object shape and structure. Among these techniques include 2D texture and photo mapping, environment mapping, range images for image-based rendering, 2D mip-mapping, video streams, 3D volumes, 3D mip-mapping, 4D light fields and lumigraphs, and five-dimensional (5D) plenoptic functions. All these techniques require some sort of dimensionality-based interpolation (bilinear, trilinear, quadrilinear, etc.) between discrete pixels, texels, voxels, or n-oxels.
Special purpose computer architectures and methods for volume visualization are known in the art. Traditional methods of volume visualization typically operate by scanning through a volume dataset in a sequential manner in order to provide an accurate representation of an object. For example, Cube-4, an architecture developed by Dr. Arie Kaufman, Ingmar Bitter and Dr. Hanspeter Pfister, some of whom are also named inventors in the present application, is a special purpose scalable volume rendering architecture based on slice-parallel ray-casting. Cube-4 is capable of delivering true real-time ray-casting of high resolution datasets (e.g., 10243 16-bit voxels at 30 Hertz frame rate). However, Cube-4 cannot deliver such real-time performance for perspective projections. Presently, in known prior art rendering systems, the use of perspective projections either increases the rendering time or decreases the projected image quality. Additionally, prior architectures do not provide the ability to combine volumes and geometries into a single image.
Referring now to FIG. 1, a conventional volume visualization system 1 is shown. As illustrated in FIG. 1, the volume data is stored on a disk 2 and loaded into memory 4 before rendering. A Central Processing Unit (CPU) 6 then computes the volume rendered image from the data residing in memory 4. The final image is written to a frame buffer 8, which is typically embedded on a graphics card, for displaying on a monitor 9 or similar display device.
The present invention, therefore, is intended to provide a method and apparatus which significantly enhances the capabilities of known methods and apparatus to the extent that it can be considered a new generation of imaging data processing.
Other and further objects will be made known to the artisan as a result of the present disclosure, and it is intended to include all such objects which are realized as a result of the disclosed invention.